1. Field of the Invention
This invention relates to the production of polyols that are useful in the preparation of rigid polyurethane and polyisocyanurate foams. More particularly this invention relates to aromatic polyester polyols made from reacting recycled polyethylene terephthalate with a solution of low molecular weight polyols and ethoxylated methyl glucoside.
2. Description of the Related Art
Rigid polyurethane or polyisocyanurate foams generally have good insulating properties and are thus desirable for use in building insulation. As with all building materials, it is desirable to provide rigid foams that are as fire resistant as possible. One approach to this goal is to modify the polyol.
Polyisocyanurate foams are generally fire resistant and show low smoke evolution on burning. However, polyisocyanurate foams tend to be brittle or friable. While various types of polyols have been devised as additives to lower the foam friability, frequently the fire and smoke properties of the polyisocyanurate foam deteriorate. Thus, a fine balance exists between the amount and type of polyol one reacts with a polyisocyanurate foam formulation in order to maintain maximum flame and smoke resistance while at the same time improve foam friability.
Scrap polyalkylene terephthalate, such as polyethylene terephthalate (PET) has been used to advantage by incorporation into polyurethane and polyisocyanurate foams. U.S. Pat. No. 4,604,410 discloses a method for making rigid polyurethane and polyisocyanurate foams which entails reacting an excess of an organic polyisocyanate with an etherified modified aromatic polyol. The etherified modified aromatic polyol is prepared by digesting scrap polyalkylene terephthalate polymers with a low molecular weight polyol, such as diethylene glycol. The resulting product is then blended with a low molecular weight polyol, such as alpha methyl glucoside. The intermediate product is etherified with propylene oxide and/or ethylene oxide.
U.S. Pat. No. 4,701,477 discloses a method for preparing polyester-polyether polyols from polyalkylene terephthalates. This method entails reacting a polyalkylene terephthalate with a low molecular weight polyol, such as diethylene glycol. The reaction product is then blended with an aliphatic polyol such as methyl glucoside. The resulting product is then reacted with an alkylene oxide such as ethylene oxide or propylene oxide to prevent solidification of the methyl glucoside, PET reaction product.
U.S. Pat. No. 4,469,824 teaches a method for making liquid terephthalic esters that are useful as polyol extenders in rigid polyurethane foams and as the sole polyol component in polyisocyanurate foams. The terephthalic esters are made to remain in a liquid form by reacting recycled or scrap polyethylene terephthalate with diethylene glycol and one or more oxyalkylene glycols. Ethylene glycol is then stripped from the reaction to yield a mixture of esters which is free from solids upon standing. Due to solubility limits, a maximum of 5 % alpha-methyl glucoside may be added to increase the functionality of the resulting product.
U.S. Pat. No. 4,644,019 discloses a method for preparing an isocyanurate foam that is similar to the methods disclosed above but this method includes reacting an ethoxylate of an alkylphenol, preferably nonylphenol, with the polyethylene terephthalate while it is being digested. The addition of ethoxylated alkyl phenols enhances the solubility of hydrocarbonfluorocarbons, such as Freon 11, in subsequent foam formulations.
Both the fire resistance and the insulation value of polyurethane and polyisocyanurate foams can be increased by expanding the foams with hydrocarbonfluorocarbons (HCFCS). However, the use of HCFCS renders the foams soft, with poor dimensional stability when exposed to cold temperatures. Practitioners have tried to overcome these drawbacks by increasing the functionality of the foams. However, when high functionality and high aromatic content are combined the usefulness of the resulting polyols is lost because their viscosity increases beyond the capabilities of the equipment commonly used for manufacturing the foams.
The novel polyol of this invention solves the aforementioned problems. By combining ethoxylated methyl glucoside or propoxylated methyl glucoside with a polyethylene terephthalate base polyester a polyol is formed which exhibits both high functionality and a high aromatic content at a conventional viscosity.